Thread cutting device for lockstitch sewing machines



March 31, 1970 H. HAGEMEYER ErAL 3,503,355

THREAD CUTTING DEVICE FOR LOCKSTITCH SEWING MACHIN' 2 Sheets-Sheet 1 Filed Oct. 1, 1968 INVENTORSZ ////vz HAGIFMEYEIP) aim/414w a/m M24159 6 I Y M J. M

HTTABAIY March 3'1, 1970 H, AGEM EY-E'R AL 3,503,355

THREAD CUTTING DEVICIE FOR LOCKS'I'ITCH SEWING MACHINES Filed Oct. 1, 1968 2 Sheets-Sheet 2 4 44 A True HEM United States Patent Int. Cl. nosb 65/00 US. Cl. 112-252 4 Claims ABSTRACT OF THE DISCLOSURE A lockstitch sewing machine having at least one stitch forming means with a horizontal lockstitch looper, a thread cutting device for cutting off the needle and looper threads below a workpiece after completion of a sewing operation. The device is provided with a thread catcher means for back and forth movements along a path extending in a horizontal plane above the looper means. Stationary counter knife means in combination with thread clamping means are provided opposite the lug means for the bobbin case holder means. Thread catcher means are provided which move out of a normal position between the counter knife means and the thread clamping means into a position for catching the threads and return with the caught threads to the normal position.

Background of the invention The invention relates to thread cutting means for lockstitch sewing machines, particularly for the type having a lockstitch looper of the vertical axis rotary type in which a bobbin case holder is journaled in a raceway of, and is restrained against rotation with, the looper, and thread catcher means which cooperates with a stationary counter knife, in a horizontal plane above the looper.

There are already known thread cutting devices for sewing machines of the above-mentioned type, wherein the thread catcher has an end or other portion of V- shaped configuration defined by a pair of legs adapted to simultaneously seize the looper thread and the needle thread, and a plunger aperture at the intersection of the legs for receiving the cutter, which the plunger aperture and the legs are disposed in a plane extending substantially parallel to the looper shaft. Such a device is disclosed in British Patent No. 976,208 published on Nov. 25, 1964.

Since the thread catcher in this known device remains in a normal position which is outside of the thread cutter and clamping means, and only engages with these for a short time to cut off the threads, it is possible to damage the comparatively sensitive thread cutter and clamping means when replacing the bobbin. This operation can be hindered when the thread catcher is in the path.

The primary object of the invention is to provide a thread cutting device for lockstitch sewing machines of the above-mentioned type which will assure the free access to the looper when changing the bobbins.

It is a further object of the invention to provide a thread cutting device for lockstitch sewing machines of the above-mentioned type which will prevent damage to the relatively sensitive stationary thread clamping and cutting means when changing the bobbins.

Summary In accordance with the main feature of the invention, there is provided in a lockstitch sewing machine having at least one lockstitch looper of the vertical axis rotary hook type, at least one thread cutting device means for cutting off the threads below a workpiece, including "ice thread catcher means above the looper, swingable in a horizontal plane, a stationary counter knife cooperating with the thread catcher, thread clamping means cooperating with the thread catcher, and an actuating means for the thread catcher, while the stationary counter knife with the thread clamping means are arranged out of the path of motion of the looper and opposite the lug means for the bobbin case holder. The actuating means move the thread catcher out of a normal position between the stationary counter knife and the thread clamping means into a position for catching the threads and for returning it with the caught threads to its normal position,

Other or more specific objects and features of the invention will be apparent from the following description of the preferred embodiment, when read in connection with the accompanying drawings.

Brief description of the drawings FIG. 1 is a top plan view of the thread cutting device with the controllable driving device;

FIG. 2 is a partial top plan view of the thread catcher, the stationary cutting knife and the thread clamping device on an enlarged scale, according to FIG. 1;

FIG. 3 is a perspective partial view of a sewing machine with the thread catcher in its normal position, and

FIG. 4 is a reduced partial view, according to FIG. 3, with the thread catcher while catching the needle thread and the looper thread.

Description of the preferred embodiment The looper driving shaft 2 pivoted in the bedplate 1 of a sewing machine drives the lockstitch looper 3 rotating about a vertical axis through a bevel gearing (not shown).

In the looper 3 there is supported the bob-bin case holder 4 which is provided with a lug 5 for preventing a rotary motion. For this purpose the lug 5 engages in a slit formed by two stops 7 in the throat plate 6, An opening finger 8 bears against the extension 9 of the bobbin case holder 4, to form a slit between the lug 5 and the stops 7, which will prevent a rotary motion of the bobbin case holder 4, to permit the passage of the needle thread 10 through this slit.

Pivoted in a carrier part 11 secured to the bedplate and taking up the lockstitch looper 3 and its driving parts, there is a thread catcher carrier 12. Secured to it by means of screws 14 is a thread catcher 13, which is formed at its free downward angled end 16 (FIG. 2) with a part 17, for catching the needle thread 10 and the looper thread 15, and with a cutting edge 18.

Out of the path of motion of the looper 3 and opposite the opening finger 8 there is arranged a stationary counter knife 19, which cooperates with the cutting edge 18 of the thread catcher 13, and a thread clamping device. It consists of a spring plate 20 which, during the normal position of the thread catcher 13, is under tension and abuts against the inner surface 21 of the thread catcher end parts 16, 17, and clamps the thread or the threads 10, 15 between itself and the inner surface 21. A rocking lever 23 is clamped to the thread catcher driving shaft 22 (FIG. 1). A linkage 24 is connected with the rocking lever 23 and a lever 25. This lever 25 is pivoted on the carrier part 11 and is provided with a roller 26, which can be made to abut on the front surface of a cam disc 27 against the tension of a spring 28. A solenoid 29 is linked with the free end of the lever 25.

The operation of the thread cutting device can be described as follows:

In the rest position of the sewing machine and during sewing, the thread catcher 13 is in its normal position, as shown in FIGS. 1 to 3, while its downwardly angled end 16 lies between the stationary counter knife 19 and the thread clamping means 20. In this position the bobbin case can be taken out of the bobbin case holder 4 for changing a bobbin without any hinderance, since the thread catcher 13 does not obstruct this removal.

In this normal position of the thread catcher 13, the danger of damaging the thread clamping means 20, which is a relatively thin spring plate, is eliminated since the thread clamping means 20 is nearly completely covered at its most sensitive part by the thread catcher 13.

For cutting the needle thread and the looper thread below the throat plate 6, the solenoid 29 is energized a short time before the sewing is terminated, while the roller 26 abuts against the front surface of the cam disc 27 which rotates with the looper driving shaft 2.

As the roller 26 falls into the recess 30 (shown in FIG. 1 by a dotted line) of the cam disc 27, the thread catcher 13 is swung over the looper at a moment, when the thread catcher 13 can still catch the needle thread loop dropped by the looper 3, where it leads to the workpiece 31. The

rising part 32 of the cam disc 27 effects the catching of (FIG. 3) rests in the thread clamping device 20, until the new stitch is formed.

It is to be understood that the herein described preferred embodiment of the thread cutting device as applied to a single needle lockstitch sewing machine is not intended to be limited to such a machine but that it may be applied to a two-needle lockstitch sewing machine of the described type, and that it is only illustrative of the possible realizations of the presently disclosed inventive concept.

What we claim is:

1. In a lockstitch sewing machine having lockstitch looper means with a bobbin for delivering a looper thread, a bobbin case holder provided with a lug for holding stationary, a vertical looper shaft carrying said looper means, a horizontal drive shaft for said looper means at least one needle for supplying a needle thread and cooperating with said looper means, a feeding device for the workpieces to be sewn, a thread cutting means for cutting off the threads below a workpiece, said cutting means including thread catcher means arranged above said looper means and swingable in a horizontal plane, stationary counter knife means cooperating with said thread catcher means, thread clamping means cooperating-with said thread catcher means, actuating means for said thread catcher means, operable when said needle is in a high position, said stationary counter knife means with said thread clamping means arranged out of the path of motion of said looper means and opposite of said lug for said bobbin case holder, said actuating means arranged for moving said thread catcher means out of a normal position between said stationary counter knife means and said clamping means into a position for catching said threads and removing the catcher means with the caught thread into the normal position for cutting and clamping the threads. I

2. In a lockstitch sewing machine as claimed in claim 1, in which said actuating means for said thread catcher means includes a cam disc arranged on said drive shaft for said looper means, a lever provided with a roller abutting against said cam disc, a rocking lever connected with said thread catcher means, linkage means between said lever and said rocking lever, and traction means articulated to said lever.

3. In a lockstitch sewing machine as claimed in claim 2, in which said traction means consists of a solenoid.

4. In a lockstitch sewing machine as claimed in claim 2, in which a spring is attached to said lever, to keep said roller out of the zone of contact of said cam disc and said thread catcher means in the normal position between said stationary counter knife means and said thread clamping means when said traction means is uncontrolled, said spring being attached to said lever.

References Cited UNITED STATES PATENTS 1,876,538 9/1932 Althens 1l2252 3,211,117 10/1965 Speichermann et al. 112-252 3,371,633 3/1968 Hedegaard 1l2252 ALFRED R. GUEST, Primary Examiner 1 

